The following is a lightly edited exchange of emails regarding the Xantrex XC3012 battery chargerís feasibility for use with absorbed glass matt (ďAGMĒ) batteries. It also touches on the use of that model of battery charger with flooded lead acid batteries (4Ds and golf cart). A question, possibly unresolved in the exchange, is whether the XC3012 could be used satisfactorily with AGM batteries if the AGM batteries are combined in one house bank (a combination of batteries often recommended at this site - see for example postings by Maine Sail) and the XC3012 is not used to charge any other battery bank. The exchange took place in May, 2012, between John Nixon and Michael MacLeod and was a follow up to Johnís battery charger evaluation, the full text of which, as posted by Stu Jackson, is at http://c34.org/bbs/index.php/topic,4352.0.html.

Michael: Towards the end of your [evaluation of] the merits of the [Xantrex] XC3012/5012 [models of battery charger] you had mentioned that you had some reservations about the use of that charger with AGM batteries, that you were in communications with Xantrex about your concerns, and that you would or might post more about the issue when you knew more. Or at least that is my recollection. Did you ever post more on that issue? I have searched but not found it if you did. If you did not post more but would be willing to do so that would be great.

John: I never got around to following up on that posting, but this will encourage me to do so :-)

Basically, Xantrex agreed that it did what I complained that it did with AGM batteries, swapped out the XC3012 I bought for the evaluation with a Truecharge2 40 amp unit with remote control panel in exchange, and said "Thank you for your observations and concerns. Now go away...."

I might poke a stick in their eye again just for the fun of it to see if they have changed their story any in the intervening time since my last discussion. I'll let you know either directly or via an update to the article.

Michael: Thank you for getting back to me on this point. We had bought the XC3012 just before you did your review of it ...and were relieved when you came out somewhat more in favour of it than you had anticipated. But now thinking about going to AGMs, it has given us pause! I donít know what your specific concern was but will watch c34.org in hopes of seeing your follow up.

John: In a nut shell, once the AGM batteries are fully charged, the pulsing action of the charge rotation/multiplexing between banks creates dangerously high float voltages on the AGM batteries. I watched "float" voltages of up to 16 to 17 volts on each bank of AGM batteries. In addition, the high float voltage drove the charger crazy.... The whole charging process in software was not well conceived.

Xantrex finally did admit that they never actually tested the charger with anything other than flooded cells during its development process, regardless of the battery setting. As a result, it had issues with both AGM and Gel technologies. The lower recharge efficiency and much higher self discharge characteristics made a poorly conceived multiplexed pulsing charge idea appear to work with flooded cells but not with newer technologies.

Michael: Thank you and yikes! This may rule out our getting AGM batteries so long as we are using the XC3012. I may investigate golf cart batteries as an alternative to our 4Ds.

John: An excellent choice if you don't mind caring for them properly: regular FULL recharge, periodic equalization cycle, proper electrolyte level ( i.e. - don't over-fill with water ), and use of only distilled water.

If you plan on keeping them for a while, look at the Trojan T105 battery. 220 a-hr @ 20 hr rate, which means usually about 10-20% more than a single 4D flooded cell.

Michael: Thank you for that further information, John. I think we are likely either to stay with 4Ds (the devil we know) or go to golf cart batteries (if the battery compartment space is adequate for those batteries and battery boxes, since I donít fancy a spill of acid into the bilge). In either case, I am considering linking all the house batteries into a single bank instead of running, as we have been, two banks. In this respect, do you have any reason to think that the fluctuating charge cycle of the XC3012 (alternating fairly frequently between charging bank 1 and bank 2) is problematical when charging flooded lead acid batteries?

John: The difference between the 4D and the pair of golf cart batteries ( i.e. - Trojan T105) will be primarily the height of the 6 volt batteries versus the 4D. The 6 volts are about 2 -3 inches taller depending upon what terminals are on the comparison batteries. The 6 volts are also shallower in horizontal depth, and stacked long way end to end will be just slightly longer then the base dimension of the 4D. The 4D has a significant difference between its top overall length versus its bottom overall length. If the battery box area currently has vertical walls (rather than tapered like a plastic battery box) each pair of 6 volts will fit in the same location as a single 4D. Then, it's just a matter of height.

I would definitely put all of the house batteries in one single bank, and then have a smaller dedicated starting battery. The XC3012 will handle that OK. The multiplexed charging scheme poses no danger to the flooded cell batteries either as multiple house banks or a single house bank and a starting bank.

Michael: Thank you very much, John.

I think we will go with golf cart batteries if we can make them fit (it is going to be very tight as we have the XC3012 dual shunt located at the top of the port end of the battery compartment under the aft salon table seat) or stay with the 4Ds if we canít make the golf cart batteries fit.

We already have a separate starting battery not connect at all to the shore powered charging system and, as it is plugging along perfectly after four years, we will probably leave it that way, to be charged only when the engine is running.

Do you think we should post this exchange to the c34.org bulletin board? I certainly found it helpful.

John: Feel free to post it as I certainly have no objection.

Michael: Thanks, John. I will do that. Perhaps someone else can benefit from our exchange.

Michael: Sorry to bother you again, John. An after-thought. Would it be feasible/sensible to go to AGMs but avoid the problem of the XC3012ís buggy software by linking the house batteries all into one bank, so they all charge together and there is no cycling between banks? We were thinking of putting all the house batteries into one bank anyway and, as indicated in my previous email, I do not plan to link the starting battery to the XC3012 anyway.

John: No, I don't think it wouldnít [sic] avoid the problem created by the charging methodology, but in retrospect I don't think that I tried that specifically. The XC series will learn to "disqualify" banks that either aren't present or no longer need charging. I suppose that if only 1 bank was installed, it might stop the initial current pulse that is used to determine if a bank is present on each output, and if that happened, it might be OK.

I have no way to test that any more, however.

Michael: Interesting. We have the XC3012 set up now on only one house battery, because the other house battery died and I disconnected it. My impression is that the XC3012 now charges the one battery full time and does not hunt and peck for any other battery to charge. Perhaps I will observe it for a while to see whether this is so. Thanks again, John.

John: In theory that is what it should do. I wish now I would have explored that condition when I had the unit in evaluation.